US4421951A - Method and arrangement for signaling the transmission mode of a communication system - Google Patents

Method and arrangement for signaling the transmission mode of a communication system Download PDF

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Publication number
US4421951A
US4421951A US06/305,124 US30512481A US4421951A US 4421951 A US4421951 A US 4421951A US 30512481 A US30512481 A US 30512481A US 4421951 A US4421951 A US 4421951A
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United States
Prior art keywords
facility
signal
mode
over
unit
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US06/305,124
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English (en)
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John G. Van Bosse
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AT&T Corp
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Bell Telephone Laboratories Inc
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Assigned to BELL TELEPHONE LABORATORIES INCORPORATED reassignment BELL TELEPHONE LABORATORIES INCORPORATED ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: VAN BOSSE, JOHN G.
Priority to US06/305,124 priority Critical patent/US4421951A/en
Priority to JP57502950A priority patent/JPS58501532A/ja
Priority to DE8282902873T priority patent/DE3267704D1/de
Priority to EP82902873A priority patent/EP0088786B1/en
Priority to PCT/US1982/001172 priority patent/WO1983001169A1/en
Priority to CA000410507A priority patent/CA1177984A/en
Priority to KR8204293A priority patent/KR880000961B1/ko
Priority to ES515919A priority patent/ES8401815A1/es
Priority to GB08227185A priority patent/GB2130845B/en
Publication of US4421951A publication Critical patent/US4421951A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors

Definitions

  • This invention relates to signaling arrangements and more particularly to a method and apparatus for signaling the analog and digital data operating modes of a communicating system.
  • the customer signal changes in the system operating mode to the local office by dialing special codes and awaiting a confirmation signal from the local central office.
  • the operating mode signaling from the customer to the local office exists as either frequency tones or digital data characters.
  • frequency tones are used for mode signaling a tone receiver is required at the local office.
  • digital data characters are used for mode signaling, a digital data receiver is required at the local office.
  • Both the frequency tone mode signaling and digital character signaling arrangements require using the same loop facility used for the transmission of the voice or digital data information. To prevent interference with the voice or digital data signals mode, signaling must be done at a time when no voice or digital data signals are on the loop facility.
  • system memory must be utilized to remember the system operating mode. Additionally, this memory must be accessed each time the operating mode information is required by the telephone network.
  • the above tone or digital character signaling arrangements result in additional complexity in the circuitry of a shared voice/digital data system which share a common telephone network.
  • the disclosed communication system operating mode signaling method and arrangement utilizes dc current signaling over the loop facility connecting the customer to the local central office.
  • This dc current signaling arrangement provides both continuous voice/digital data operating mode signaling and continuous on-hook/off-hook signaling over the loop facility connecting the customer unit to the central office unit.
  • the existence of a dc current flow over the loop facility indicates an off-hook condition at a customer's unit while the direction of the current flow over the facility indicates the communicating or operating mode of the system.
  • a current flow in a first direction over the transmission facility signals a system voice operating mode while a current flow in the opposite direction signals a system digital data operating mode.
  • a customer or subscriber signals a change in the system operating mode by reversing the direction of the current drain at the customer unit.
  • the resulting interruption of the dc current flow is detected by the central office unit which responds by reversing the polarity of the current source connected to the facility.
  • the reappearance of a dc current flow on the facility distinguishes a customer's change in operating mode from a customer's call termination (on-hook) condition.
  • the disclosed dc signaling arrangement is utilized as part of an alternate voice/digital data system where the customer can alternately switch an active call between the voice and digital data operating modes.
  • the customer or subscriber dials an access code and the telephone number of the called party.
  • the access code is utilized by the telephone network to distinguish a voice only call from an alternate voice/digital data call.
  • the initial connection between the calling and called customer is established in the voice mode. Once the connection is established either the calling or the called customer can change the direction of allowed current flow on the facility to the central office to initiate an operating mode change from the voice mode to the digital data mode and vice versa.
  • Timing circuits at the central office distinguish a hit or other inadvertent dc current interruption from a customer's valid operating mode change.
  • the central office responds to a valid operating mode change current interruption by reversing the polarity of the battery feed to the facility. If the current flow over the customer's facility does not resume within a predetermined time period the central office recognizes this condition as a customer on-hook condition rather than a customer request to change from a voice to a digital data operating mode. If a valid digital data operating mode is established the central office makes appropriate network changes to facilitate digital data transmission between the customers.
  • FIG. 1 shows a circuit diagram of the customer apparatus of my invention.
  • FIG. 2 shows a circuit diagram of the central office apparatus of my invention.
  • FIG. 3 shows the association of FIG. 1 and FIG. 2.
  • FIG. 4 shows a typical local call connection path between customers.
  • FIG. 5 shows the signaling bits utilized by my invention.
  • FIG. 6 shows a typical tandem call connection path between customers.
  • the apparatus located at a customer or subscriber location includes telephone set SA and data set DA which are shown connected to interface unit IUA via cables 101 and 102 respectively.
  • telephone set SX and data set DX connect to interface unit IUX via cables 103 and 104 respectively.
  • Interface units IUA and IUX connect via loop transmission facilities LA and LX, respectively, to local central office COA (shown in FIG. 2).
  • Interface unit IUA includes switch SW1 for switching or coupling the signaling (dc current) means to the facility.
  • These operating mode signaling means (D1, D2) signal a voice operating mode or a digital data operating mode of the system.
  • Diode D1 provides a means for signaling a voice operating mode to central office COA by enabling a current flow from the tip T lead to the ring R lead of loop facility LA.
  • Diode D2 provides a means for signaling a digital data operating mode to central office COA by enabling a current flow from the ring R lead to the tip T lead of loop facility LA.
  • facilities LA and LX terminate on switch SWA of central office COA.
  • Channel units CUA and CUX at central office COA also connect to switch SWA.
  • switch SWA shown in FIG. 2 is preferably a No. 1/1A ESS
  • my invention can similarly be implemented with any crossbar or step by step type of central office switch which can pass dc currents.
  • the operation of the No. 1 ESS is well known, for example see the September 1964 issue of the Bell System Technical Journal. In the description that follows only the operation of circuitry of the No. 1 ESS required for an understanding of my invention will be discussed.
  • Common control CCA enables switch SWA, in a well-known manner, to provide a communication connection between the loop facilities (LA and LX) and channel units (CUA and CUX).
  • Channel units CUA and CUX as well as common equipment CEA are part of digital channel bank DCBA.
  • Channel units CUA and CUX convert the analog voice or digital data signals from customer A and X into a digital format for transmission over a digital carrier (e.g. T1 carrier) line T1. While a T1 carrier is described herein, other digital carrier systems can obviously be utilized.
  • Carrier line T1 connects central office COA with other central offices.
  • Common equipment CEA of digital channel bank CBA multiplexes the signals from channel units CUA and CUX onto interoffice T1-carrier line T1.
  • the operation of a typical digital channel bank is described in U.S. Pat. No. 4,059,731 issued on Nov. 22, 1977 to Green et al which is incorporated by reference herein. Only the operation of circuitry of the channel unit required for an understanding of my invention will be discussed herein.
  • Channel units CUA and CUX utilized in the disclosed invention include voice hybrid VH which establishes, during a voice operating mode, a first direction of current flow (from T and R lead) over loop facilities LA and LX. Also included is digital data hybrid DH which establishes, during a digital data operating mode, a direction of current flow (from R to T lead) over loop facilities LA and LX.
  • Relay R1 detects interruption of loop current flow.
  • Relay R2 provides a means for switching between the voice hybrid VH and digital data hybrid DH or vice versa in response to a current interruption signal from relay R1.
  • Loop status circuit is responsive to a continued interruption of loop current to cause a termination of the voice or data operating mode by appropriately signaling common control CCA.
  • Common control unit CCA of FIG. 2 can be implemented as a separate computer controller operating under program control or can be incorporated as part of the controller for either switch SWA or digital channel bank DCBA.
  • common control unit CCA controls channel units CUA and CUX, common equipment CEA, and switch SWA to enable the various call connections through central office COA.
  • a telephone call is initiated when a subscriber or customer A places telephone set SA in an off-hook condition.
  • the on-hook to off-hook transition occurs only during a voice operation mode.
  • customer A places interface IUA in the voice mode by setting switch S1 to the voice position V.
  • Switch SW1 provides a control for customer A to switch between the voice and digital data operating modes. Switch SW1 could be made to switch to the voice mode automatically when customer A goes off-hook.
  • central office COA when central office COA detects current flow from the T to R leads it performs the well-kown normal loop tests (power cross, etc.) and connects a switching path 401 through switch SWA between customer A and a digit receiver (DR) 420. Digit receiver 420 provides a dial tone to customer A.
  • DR digit receiver
  • Customer A starts dialing (using rotary dialing or TOUCH-TONE dialing) when dial tone is received.
  • Customer A dials the alternate voice/digital data V/D accesss code to indicate to central office COA that customer A desires to send voice or digital data over loop A. Thereafter, customer A dials the telephone number of customer B located at a second central office COB.
  • common control CCA of central office COA seizes a channel unit CUA of an outgoing trunk of carrier facility T1 to central office COB. Since not all customer facilities at central office COA are provided with the disclosed alternate voice/digital data V/D capability central office COA must detect the V/D access code on an originating call and then connect it to a channel unit CUA and trunk having the V/D capability.
  • the receiving central office COB knows a V/D call is being received since a V/D trunk is being utilized.
  • Common control CCA sets up a switching connection 402 between digit transmitter (DT) 421 and channel unit CUA.
  • Central office COB detects a seizure of an incoming trunk and sets up a switching connection 404 to a digit receiver (DR) 422. Digit transmitter (DT) 421 of central office COA sends dialed digits to receiver 422 of central office COB. When the dialed digit transfer is complete central office COA releases switching connections 401 and 402 and establishes switching connection 403. Central office COB releases switching connection 404 and establishes switching connection 406 which connects a ring generator 423 to loop LB of the called subscriber or customer B. Central office COB also sets up connection 407 to provide an audible ringing signal back to customer A.
  • DR digit receiver
  • DT Digit transmitter
  • Central office COB releases switching connection 404 and establishes switching connection 406 which connects a ring generator 423 to loop LB of the called subscriber or customer B.
  • Central office COB also sets up connection 407 to provide an audible ringing signal back to customer A.
  • voice circuit V1 provides the means for communicating voice signals over facility LA during the voice operating or communicating mode. It is to be noted that switch SW1 switches the facility current through either voice circuit V1 or digital data coupler 107. While the disclosed arrangement shows telephone set SA powered directly from loop LA, it is contemplated that telephone set SA could be powered at the customer or subscriber location with appropriate switch contacts and circuitry to provide the disclosed signaling functions.
  • the channel units encode the mode information as signaling bits of the T1-carrier signal.
  • the channel units CUA and CUB are in a "local" state and connect respectively to customer interface IUA and IUB.
  • Channel units CUA and CUB also connect to T1-carrier facility T1.
  • Carrier facility T1 is also referred to herein as carrier line T1 or carrier trunk T1.
  • the operating mode of each channel unit (CUA or CUB) connected to a carrier facility (T1) at an end office (originating office COA or terminating office COB) should always follow the operating mode of each interface (IUA or IUB) connected via the associated loop facilities (LA or LB).
  • LA or LB associated loop facilities
  • the channel units CUA and CUB detect the operating mode of these respective interface units IUA and IUB by determining the direction of current flow on the respective loops LA and LB.
  • Channel units CUA and CUB inform each other of their operating mode by encoding bit 8 of frame 6 and 12 of the outgoing T-carrier signal on carrier trunk T1.
  • bit 8 of frame 6 of each superframe is referred to as bit A while bit 8 of frame 12 of each superframe is referred to as bit B.
  • the channel unit CUA sends either Far-End-Voice (FEV) control mode characters or Far-End-Digital (FED) tone to its interface (IUA) to indicate the state of the far end customers interface (IUB).
  • FEV Far-End-Voice
  • FED Far-End-Digital
  • a channel unit determines a conflict by comparing its own mode (which follows the mode of the connected IU) with the A and B bit pattern that it is receiving over the T-carrier facility T1.
  • relay R2 is operated over lead 211 and the make contacts of transfer contacts R2-1 and R2-2 connect voice hybrid VH to line 201.
  • channel units CUA and CUB are connected in a local state connection lead TAN out of common control CCA is at ground and hence relay R5 is not operated.
  • the break contact of R5-3 remains closed enabling loop control 206 to control relay R2.
  • Analog voice signals from voice hybrid VH are sampled and pulse amplitude modulated (PAM) by converter A/P and are transmitted as signal TPAM to common equipment CEA.
  • Common equipment CEA converts the PAM signal into a pulse coded modulation PCM signal which is then modulated as one of the channels of the T-carrier data stream shown in FIG. 5.
  • loop status circuit 205 receives the status of loop LA and indicates the on-hook/off-hook status over lead SL to common control CCA.
  • relay R1 of loop current monitor 200 is operative and make contact R1-1 puts a ground potential on lead 203 to loop status circuit 205.
  • loop status circuit 205 receives signal TS when a mode transition from a voice to digital or vice versa is occuring on loop LA.
  • loop status circuit 205 provides an off-hook signal over lead SL to common control CCA. Otherwise loop status circuit 205 transfers the on-hook status over central lead SL to common control CCA.
  • Control signals DS and VS from loop control circuit 206 indicate, respectively, the digital or voice operating mode of customer A. Since channel unit CUA is in the local state, as noted previously, relay R5 is not operated and the break contacts of R5-1 and R5-2 remain closed.
  • PCM digitized voice which is converted to pulse amplitude modulated voice signal and placed on lead RPAM.
  • a signal exists on lead V/D indicating such a condition to common equipment CEA of digital channel bank DCBA.
  • digital channel bank DCBA accepts the PCM signal on lead T8B for transmission over carrier facility T1 and the received PCM signals are outputted on lead R8B.
  • Voice signals received from customer B over facility T1 are converted from a PCM signal to a PAM signal RPAM by common equipment CEA.
  • a PAM to analog converter P/A reconstructs the voice signal for transmission through voice hybrid VH, line 201, switch SWA to customer A via loop LA.
  • Trunk control 208 monitors the bit 8 pattern received on line RB8 from common equipment CEA.
  • Conflict circuit 209 includes relays R3 and R4 which indicate respectively voice or digital mode conflicts.
  • signal VS Since customer A is in a voice mode, signal VS is logic 1, if a voice mode signal VT is also logic 1 no conflict exists and relay R3 is not operated and the make contact of transfer contact R3-1 is open and prevents a far-end-digital FED tone from being outputted to customer A. However, if customer B is in a digital mode, signal VT is logic 0 and relay R3 is operated and break contact of R3-1 opens to prevent signals from customer B via unit P/A from reaching voice hybrid VH and customer A. Additionally, a FED tone from unit 215 is connected by the make contact of R3-1 to voice hybrid VH and customer A. The FED tone alerts customer A that customer B is in the digital data mode.
  • trunk status circuit 210 also receives the bit A and B status over leads RA and RB and generates a trunk status signal ST for common control CCA.
  • Either customer A or customer B can initiate a change from the established voice connection to a digital data connection.
  • customer A switches to the digital mode.
  • customer A sets the operating mode selection switch SW1 to the digital data position D.
  • the current flow from lead T through the mode switchhook contact SH, switch SW1, diode D1, dial contact DC, voice circuit V1 to lead R is interrupted.
  • the presence of diode D2 in the digital position path prevents current from flowing from the T lead to the R lead of loop LA. While diodes D1 and D2 are illustrated as implementing circuits to selectively enable a certain direction of current flow over loop LA other circuits (transistors, etc.) are known to implement such characteristics.
  • loop current monitor 200 detects an interruption of current on line 201 which is connected through switch SWA to loop LA.
  • relay R1 detects the interruption and releases causing make contact of R1-1 to open and an ungrounded signal to appears on lead 203.
  • An interruption of current is an indication to channel unit CUA that either (1) a mode change command is being sent (2) that customer A has gone on-hook or (3) that a hit has occurred on loop LA.
  • Current monitor 200 incorporates a timer or delay 212 which waits an appropriate length of time to insure that a hit has not occurred before changing the state of relay R2.
  • the combination of relay R1, control circuit 206 and relay R2 provide a means for alternating the connection of voice hybrid VH and digital hybrid DH which generate the two directions of current flow over facility LA.
  • circuit of loop control circuit 206 releases relay R2 and starts timer 213 which causes a logic 1 signal TS on lead 204 for a timed interval. If the current on loop LA reappears before timer 213 expires then the condition is regarded as a mode change request. However, as will be discussed later if the current on loop LA does not reappear, the condition is an on-hook condition by customer A.
  • the TS signal into loop status circuit 205 keeps an off-hook signal condition on lead SL to common control CCA.
  • a termination or on-hook signal condition from circuit 205 to common control CCA does not result because of the timed or delayed transition signal TS on lead 204.
  • relay R2 releases the make contacts of R2-1 and R2-2 are opened and the tip to ring current generated by the connection of voice hybrid VH to line 201 is terminated.
  • a connection is established between digital hybrid DH and line 201 via the break contacts of R2-1 and R2-2.
  • Relay R2 provides a means for connecting either the voice hybrid VH or the digital hybrid DH to facility LA.
  • Relay R2 is operative from control signal 211 which is produced by control circuit 206.
  • loop LA has -V on its T lead and a ground on its R lead.
  • a current flow exists from lead R through coupler 107, diode D2 and make contact M of switchhook SH to lead T.
  • This direction of loop current flow at subscriber interface IUA signals a digital data operating mode to central office COA. Since no current flows through voice circuit V1 telephone set SA is inoperative.
  • Data unit DA is now connected to loop LA via receive circuit 105, send circuit 106 and coupler 107.
  • loop control 206 signals common control CCA via the logic 1 on lead DS that a digital mode has been established by customer A.
  • Loop control 206 signals digital hybrid DH that a voice-to-digital transition has been initiated by customer A. Thereafter, digital hybrid DH and interface IUA go through an automatic balance sequence. The details of this balance sequence is not necessary to the understanding of the disclosed invention.
  • a conflict circuit (equivalent to 209 of channel unit CUA) detects that customer B is in the voice mode (VS is logic 1) and customer A is in the digital mode (VT is logic 0). Consequently, conflict relay R3 of channel unit CUB operates causing a FED tone to be outputted via make contact of R3-1 to customer B.
  • Customer B receives the FED tone over the receiver of its handset (equivalent of HA of telephone set SA of FIG. 1). Customer B then decides whether it wants to switch to a digital mode.
  • FEV far end voice
  • a FEV character is sent to customer A via the make contact of R4-1 when relay R4 of conflict circuit 209 operates.
  • Relay R4 operates when it receives a logic 1 on lead DS while a logic 0 is on lead DT. Lead DS being logic 1 since customer A has switched to the digital mode and lead DT being logic 0 since customer B is still in the voice mode.
  • the FEV signal is received from coupler 107 by FEV detector 108.
  • Detector 108 causes lamp 109 or other indicator to turn on indicating that the far end customer B is in the voice mode.
  • customer A can wait a few moments for customer B to switch to the digital mode or can return to the voice mode.
  • the digital hybrid DH, transmit data circuit TD, and receive data circuit RD communicate digital data between loop LA (via line 201) and common equipment CEA. Transmit data circuit TD outputs a 8-bit PCM data word over lead T8B.
  • Common equipment CEA multiplexes the digital data from lead T8B into T-carrier format, of FIG. 5, for transmission over carrier facility T1. The digital data from common equipment CEA is demultiplexed into a 8-bit PCM data word on lead R8B which is coupled to receive data circuit RD.
  • current monitor 200 of channel unit CUA continuously monitors current flow over loop LA.
  • the direction of current flow on loop LA gives a continous indication of the digital operating mode of customer A.
  • the direction of current flow over loop LB gives channel unit CUB a continous indication of the operating mode of customer B.
  • channel unit CUA continuously knows the operating mode status of customer B by virtue of the continous pattern of signaling bits A and B received over carrier facility T1 from channel unit CUB.
  • channel unit CUB continuously knows the operating mode of customer A by virtue of the continous pattern of signaling bits A and B.
  • the operating mode status of both customer A and customer B is constantly available from the above signal conditions on loop LA, loop LB and carrier facility T1.
  • relay R1 of current monitor 200 is released by the interruption of current flow.
  • timer 213 in loop control circuit 206 When make contact R1-1 opens, timer 213 in loop control circuit 206 generates a transition signal TS on lead 204 to enable loop status circuit 205 to temporarily maintain an off-hook signal SL to common control CCA.
  • Loop control circuit 206 operates relay R2 which disconnects digital hybrid DH and reconnects voice hybrid VH resulting in a battery reversal across the T and R lead of line 201 and hence loop LA. Since customer A has gone on-hook at telephone set SA current flow remains interrupted on loop LA when battery is reversed. After a continued current interruption on loop LA lasting a predetermined period of time, timer 213 of loop control circit 206 times out and transition signal TS disappears from line 204.
  • Channel unit CUA reverts to the voice mode when it is idle (on-hook).
  • current monitor 200 detects the current interruption and releases relay R1. Again timer 213 of loop control circuit 206 outputs a transition signal TS to loop status circuit 205. Loop status circuit 205 maintains an off-hook signal SL to common control CCA. Loop control circuit 206 also operates mode switching relay R2. The operation of relay R2 disconnects data hybrid DH and connects voice hybrid VH causing a battery reversal on the T and R leads of loop LA via line 201 and switch SWA. When current flow resumes on loop LA in a direction from lead T to lead R relay R1 operates. When relay R1 operates make contact R1-1 closes and timer 213 of loop control circuit 206 is reset.
  • Loop control circuit 206 outputs a logic 1 signal on lead VS and a logic 0 signal on lead DS signifying a voice operating mode for customer A.
  • Conflict circuit 209 receives the logic 1 on lead VS and releases relay R3 if a logic 1 signal exists on lead VT.
  • R3-1 If customer B has not switched to the voice mode lead VT has a logic 0 signal and relay R3 of conflict circuit 205 is operated. Consequently, make contact of R3-1 permits a FED (far end digital) tone to be outputted through voice hybrid VH to customer A. Thus, customer A knows of the status of his request to change from the digital to the voice operating mode.
  • relay R3 releases and make contact R3-1 connects the signals received from customer B, via lead RPAM and converter P/A, to customer A.
  • channel unit CUB (not shown) the transition of customer A from a digital mode to a voice mode results in a FEV (far end voice) control mode character being sent to customer B until customer B changes to the voice mode.
  • a FEV character results because channel unit CUB is in the digital mode while channel unit CUA is in the voice mode.
  • interface IUB the FEV character results in a visual output FEV signal to customer B.
  • customer B After customer B has made the transition from the digital to the voice mode channel unit CUA and channel unit CUB signal respectively customer A and customer B indicating that a voice connection is complete. Note that equalization or balancing of the voice hybrids is not required on transactions to the voice mode. Voice communication between customer A and customer B ensues.
  • channel unit CUA During the voice operating mode the direction of current flow from the T lead to the R lead of loop LA gives channel unit CUA a continuous indication of the operating status of customer A via interface IUA.
  • channel unit CUB has a continuous status indication of customer B and customer A.
  • customer A or customer B can request a change to the digital operating mode or hang-up.
  • FIG. 6 illustrates a connection between a customer A at central office COA and a customer D at central office COD, involving two tandem switching offices COB and COC.
  • COB is a No. 1A ESS
  • COC is a No. 4 ESS.
  • the end offices COA and COB are again assumed to be No. 1A ESS switches.
  • Customer A is connected to office COA via interface unit IUA and customer D is connected to office COD via interface unit IUD.
  • channel units CUA and CUD are in a "local” state since they are connected directly to the customer's two-wire facilities (loops LA and LB).
  • channel units CUB 1 and CUB 2 are in a "tandem" state since they are connected by the switching network SWB.
  • FIG. 2 shows this indication as the presence of a voltage on lead TAN, which operates relay R5. This causes CUA to be in a tandem state.
  • circuit 206 no longer controls whether hybrid DH or hybrid VH is connected to the two-wire port.
  • This mode control is now achieved by circuit 208 (via relay contacts R5-3) which receives the analog/digital mode indication on RB8 from the T1 line, and operates or releases relay R2.
  • a channel unit when a channel unit is in a "tandem" state, it connects hybrid DH or hybrid VH and the associated DC polarities on the T and R leads of the two-wire port, as dictated by the mode indication on the incoming T1 bit stream.
  • the channel unit uses relay R1 as a conflict indicator.
  • the channel unit uses relay R1 as a conflict indicator.
  • the operated state of R1 indicates a mode conflict
  • the released state of R1 indicates a mode agreement with the connected channel unit.
  • a channel unit When in a tandem state, a channel unit has to indicate the state of the connected channel unit to its outgoing T1 line, by presenting the proper voice/digital indication on lead V-D of FIG. 2.
  • R5 is operated.
  • the outputs of trunk control circuit 208 are connectes straight through to the inputs of circuit 207, via the break contacts R1-2.
  • the output of circuit 207 also indicates the digital mode, indicating that, because no conflict is detected, the connected channel unit is also in the digital mode.
  • circuit 208 is cross-connected to the inputs of circuit 207 via the make contacts R1-2. In this condition, a "digital" indication received on 208 results in a "voice” indication at output V-D of circuit 207. In this manner, the channel unit in a tandem connection pass the mode indication of the connected channel unit to the outgoing T1 bit stream.
  • the establishing of a call between customer A of central office COA and customer D of central office COD proceeds in the following manner.
  • a call is initiated when customer A goes off-hook at station SA.
  • Central office COA detects the tip to ring loop current (since all voice/digital calls are established in a voice mode) as previously described.
  • a digit receiver is connected to and supplies dial tone to customer A over loop LA.
  • Customer A dials the voice/digital data operating mode access code and the telephone number of customer D. Note this dialing can obviously be manually via a keypad or automatically if interface unit IUA is so equipped.
  • Central office COA collects the digits in the normal manner, determines that a voice/digital data call (V/D) is being made, and selects an outgoing voice/digital data (V/D) trunk on carrier facility T1. As noted previously, central office COA only selects V/D trunks to the other central offices once a V/D call is requested. Hence, the other central offices know a V/D call is being received since a V/D trunk is being utilized.
  • the selected facility involves channel unit CUA in office COA and channel unit CUB 1 in office COB. Since both COA and COB are assumed to be No. 1A ESS offices, the inter-office signaling can be implemented either on a per-trunk basis (using MF or any other signaling method), or by common channel inter-office signaling CCIS.
  • Office COA signals the called number to office COB.
  • VID facility to office COC is seized and office COB signals the called number to office COC. Since office COC is assumed to be a No. 4 ESS, common channel inter-office signaling (CCIS) is used between COB and COC.
  • CCIS common channel inter-office signaling
  • COC seizes a VID facility to office COD and sends the called number to COD using CCIS signaling.
  • the call arrives at COD on a facility that includes channel unit CUD.
  • Office COD establishes a connection between CUD and an audible tone circuit, and between called customer B a ringing circuit. Customer B's telephone rings and customer A hears the audible ringing tone.
  • COD connects IUD of the called customer to channel unit CUD.
  • CUA is in a local state and in the voice mode, since customer A is in the voice mode.
  • Channel unit CUD is likewise in a local state and in the voice mode because customer B is in the voice mode.
  • CUB 1 and CUB 2 are in a tandem state.
  • CUB 1 is in the voice mode because it receives the voice mode indication from CUA.
  • CUB 2 is in the voice mode because it receives the voice mode indication from CUD via office COC.
  • Trunk control circuit 208 has to determine the mode from bits 8 (on lead RB8) of the communication channel, but does not know which of these bits are really A and B bits.
  • the algorithm for detecting the mode by examining bits 8 is simple.
  • digital mode indications have all bits 8 either consistently “1” or constantly “0", while in voice on and off hook modes, bits A and B are opposed (0,1 or 1,0), while the other ten occurances of bit 8 during a super frame represent the least significant bit of the pcm encoded voice sample.
  • any consecutive group of at least 12 bits 8 must contain at least one "1" and at least one "0” since it must contain an A and a B bit.
  • such a group can consist of all "1”s or all "0”s.
  • Those skilled in the art may utilize various embodiments of this basic algorithm to implement the function of circuit 208.
  • interface unit IUA and channel unit CUA permit current flow from the tip lead T to the ring lead R.
  • Channel unit CUB 1 and channel unit CUB 2 both have the tip lead T at a ground potential at the ring lead R at -48 V. Hence, no current flows between channel unit CUB 2 and channel unit CUB 1 (i.e., no conflict).
  • Channel unit CUD and interface unit IUD permit current flow from the tip lead T to the ring lead R.
  • the voice signal is transmitted in PCM format on the T-carrier facilities and through the No. 4 ESS located at central office COC.
  • the PCM signal is converted to an analog form for transmission through the No. 1/1A ESS networks and loops associated with central offices COA, COB and COD.
  • the A and B bits have the values 1 and 0, respectively, indicating voice off-hook mode.
  • the current on loop LA is interrupted to interface unit IUA.
  • Channel unit CUA detects the loss of loop current on loop LA and reverses the battery and ground connects to loop LA, reestablishing current flow to interface unit IUA.
  • no reappearance of current on loop LA indicates that customer A has gone on-hook.
  • channel unit CUA is placed in the digital mode. At this time channel unit CUA and interface unit IUA immediately begin balancing their hybrids as previously described.
  • TIP transition in progress
  • channel unit CUA detects a mode conflict since it is in the digital mode and the incoming T-carrier signal on carrier facility T1 indicates (via A/B bits which are 1/0) that interface unit IUD is in the voice mode. Accordingly, channel unit CUA continuously generates and transmits "far end voice" (FEV) control mode characters to interface unit IUA.
  • FEV far end voice
  • channel unit CUA simply repeats the signal received from interface unit IUA on to the outgoing carrier facility T1.
  • Interface unit IUA transmits "control mode idle” (CMI) characters at this time to channel unit CUA.
  • CMI control mode idle
  • the bit 8 pattern on carrier facility T1 directed to central office B has changed.
  • channel unit CUB 1 Since channel unit CUB 1 is in off-hook state, it is able to pass this mode change information to channel unit CUB 2. This is done by reversing the battery and ground connections to the T and R leads 601, causing loop current to flow through the No. 1/1A ESS networks at COB to channel unit CUB 2.
  • Channel unit CUB 2 detects the current flow on the T and R leads (2-wire side) and thus detects that interface unit IUA is in the digital mode.
  • Channel unit CUB 2 forwards this information to interface unit IUD by generating the transmitting TIP characters on trunk T2.
  • the T-carrier bit stream on carrier facility T2 passes through the No. 4 ESS at central office COC unchanged.
  • No. 4 ESS is a time division multiplexing machine, the bytes or words may not be in the same position in the superframe.
  • the concept of A and B bits is meaningless when applied to the bit stream leaving a No. 4 ESS.
  • techniques are known to recover the necessary information from bit 8 alone without knowing the specific identify of A and B bits.
  • channel unit COD When channel unit COD detects that bit 8 is constantly 0 it signals interface unit IUD that interface unit IUA is in the digital mode. This is done by generating "far end digital" tone (FED) and sending it to interface unit IUD over loop LD. Interface unit IUD detects this tone and notifies customer D via a lamp (109 of FIG. 1) or tone signal (not shown). At this time, the two interface units are in conflicting modes, and each customer A and D is aware of the other's mode. The two interface units IUA and IUD remain in this configuration as long as customer A and D are ordering them to be in opposite modes.
  • FED far end digital tone
  • Interface unit IUD reverses the permitted direction of loop current flow on loop LD.
  • Channel unit CUD detects the loss of loop current, reverses battery feed, and detects the reestablishment of current on loop LD.
  • Interface unit IUD and channel unit CUD are now in the digital mode and initiate the balancing and the respective data hybrids.
  • This channel unit which is in a local state and is therefore in a digital mode, following the command from cutomer A, had been sending far-end voice (FEV) characters to customer A because it was recognizing a conflict between the digital mode of customer A and the voice mode indication arriving on facility T1. Since CUB 1 now starts sending a digital mode indication to CUA, this channel unit stops sending FEV characters to customer A and repeats the digital patterns received on T1 to the customer. At this point, exchange of 56 kb/s data between customers A and B can begin.
  • FEV far-end voice
  • Interface unit IUD stops sending data, and reverses the permitted direction of current flow on loop LD, and switches the station set SD on to loop LD.
  • Channel unit CUD detects the loss of loop current, reverses its battery feed to loop LD, thus reestablishing loop current.
  • Channel unit CUD switches to the voice mode by switching its voice hybrids onto loop LD and causing the transmission of PCM encoded voice over carrier facility T3 with A/B bits encoded as 1/0.
  • channel unit CUD Since the incoming T-carrier bit stream on carrier facility T3 indicates that interface unit IUA is in the digital mode channel unit CUD detects the incompatibility of the modes between interface unit IUA and interface unit IUD. Being in the voice mode itself, channel unit CUD therefore generates the "far end digital" tone (FED) and sends it to interface unit IUD, causing interface unit IUD to indicate to its customer that the far end is in the digital mode.
  • FED far end digital
  • the PCM encoded voice signal from channel unit CUD propagates through central office COC to channel unit CUB 2. Once channel unit CUB 2 has detected the change of the incoming bit 8 pattern, it switches into the voice mode. This switch involves connecting the voice hybrid on the 2-wire side of the channel unit, reversing the battery connection and interpreting the incoming signal from T-carrier facility T2 as PCM encoded voice. The battery reversal at channel unit CUB 2 causes a loop current to flow through the No. 1/1A ESS network at COB to channel unit CUB 1.
  • channel unit CUB 2 This current indicates to channel unit CUB 2 that interface unit IUA is in the opposite mode to interface unit IUD. Since channel unit CUB 2 knows that interface unit IUD is in the voice mode, due to the bit 8 pattern incoming on carrier facility T2, it determines that interface unit IUA remains in the digital mode. Thus, channel unit CUB 2 causes transmission of a PCM voice silent code on carrier facility T2.
  • channel unit CUB 1 also detects the flow of loop current.
  • Channel unit CUB 1 switches to the voice mode and causes the encoding of the incoming voice signal on its 2-wire side as PCM with A/B bits added. This PCM signal is sent out on carrier facility T1. Since the signal incoming to channel unit CUB 1 on carrier facility T1 continues to indicate that interface unit IUA is in the digital mode, the incoming digital signal from carrier facility T1 is discarded after checking its bit 8 pattern.
  • Channel unit CUB 1 transmits a voice silent signal on the 2-wire facility to channel unit CUB 2.
  • Channel unit CUA detects the changed bit 8 pattern received on carrier facility T1. Since channel unit CUA is in the digital mode, it generates a digital character (FEV) to inform interface unit IUA that interface unit IUD is in the voice mode. Channel unit CUA generates this signal and sends it on loop LA to interface unit IUA while continuing to pass data received from interface unit IUA to trunk T1. Interface unit IUA detects the incoming FEV characters and signals its customer that the distant interface unit is in the voice mode.
  • FEV digital character
  • the two interface units are in opposite modes but both are aware of that fact.
  • customer A switches interface unit IUA to the voice mode.
  • current is interrupted on loop LA.
  • Channel unit CUA detects the loss of loop current, reverses loop battery feed and switches to the voice mode.
  • channel unit A begins encoding the incoming voice from loop LA (with A/B bits added) and decoding the incoming T-carrier signal from trunk T1 into voice signals which are sent out on loop LA.
  • Channel unit CUA transmits the encoded voice over trunk T1 towards channel unit CUB 1.
  • channel unit CUB 1 detects the changed bit 8 pattern, it reverses its battery feed to its 2-wire port. This causes loop current to disappear, indicating that mode compatibility has been achieved.
  • Channel unit CUB 1 now becomes transparent to voice signals in both directions, doing the normal PAM encoding/decoding function. The loss of loop current flow has the same effect on channel unit CUB 2 causing it to become transparent to voice signals.
  • Channel unit CUD also detects the return of the bit 8 pattern to that associated with A/B bit signaling. Since it is already in the voice mode, compatibility has been achieved. Therefore, channel unit CUD stops sending a FED tone and allows voice transmission in both directions. Normal voice transmission may now take place between customer A and customer D.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Interface Circuits In Exchanges (AREA)
  • Communication Control (AREA)
US06/305,124 1981-09-24 1981-09-24 Method and arrangement for signaling the transmission mode of a communication system Expired - Fee Related US4421951A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US06/305,124 US4421951A (en) 1981-09-24 1981-09-24 Method and arrangement for signaling the transmission mode of a communication system
PCT/US1982/001172 WO1983001169A1 (en) 1981-09-24 1982-08-30 Method and arrangement for signaling the transmission mode of a communication system
DE8282902873T DE3267704D1 (en) 1981-09-24 1982-08-30 Method and arrangement for signaling the transmission mode of a communication system
EP82902873A EP0088786B1 (en) 1981-09-24 1982-08-30 Method and arrangement for signaling the transmission mode of a communication system
JP57502950A JPS58501532A (ja) 1981-09-24 1982-08-30 通信システムの伝送モ−ド用の信号方法と装置
CA000410507A CA1177984A (en) 1981-09-24 1982-08-31 Method and arrangement for signaling the transmission mode of a communication system
KR8204293A KR880000961B1 (ko) 1981-09-24 1982-09-23 통신 시스템의 전송모오드를 신호화하기 위한 방법 및 장치
ES515919A ES8401815A1 (es) 1981-09-24 1982-09-23 Procedimiento y aparato para senalizar el modo de transmision de un sistema de comunicacion.
GB08227185A GB2130845B (en) 1981-09-24 1982-09-23 Method and arrangement for signalling the transmission mode of a communication system

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US06/305,124 US4421951A (en) 1981-09-24 1981-09-24 Method and arrangement for signaling the transmission mode of a communication system

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US (1) US4421951A (ja)
EP (1) EP0088786B1 (ja)
JP (1) JPS58501532A (ja)
KR (1) KR880000961B1 (ja)
CA (1) CA1177984A (ja)
DE (1) DE3267704D1 (ja)
ES (1) ES8401815A1 (ja)
GB (1) GB2130845B (ja)
WO (1) WO1983001169A1 (ja)

Cited By (6)

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US4608686A (en) * 1982-02-22 1986-08-26 Mitel Corporation Two wire voice and data subscriber loop
US4685123A (en) * 1985-09-13 1987-08-04 American Telephone And Telegraph Company Communication system having voice and data capability
US4916607A (en) * 1986-10-02 1990-04-10 Canon Kabushiki Kaisha Computer for executing a process control program and a communication control program in parallel
US5408524A (en) * 1993-03-29 1995-04-18 Xel Communications, Inc. Answer supervision over pulse code modulated carrier system and method therefore
US5499285A (en) * 1991-11-12 1996-03-12 Microlog Corporation Automated telephone system with TDD capability
US6813353B1 (en) * 2000-04-12 2004-11-02 Adtran, Inc. Redundant operation of ring voltage generators utilizing voltage bus segmentation for fault isolation

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US4884667A (en) * 1987-07-22 1989-12-05 Isuzu Motors Ltd. Automatic change gear control means

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US3908086A (en) * 1974-06-03 1975-09-23 Redactron Corp Method for establishing a data communication connection between two full duplex modems
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US4009342A (en) * 1973-04-19 1977-02-22 Siemens Aktiengesellschaft Circuit arrangement for communication facilities wherein transmission paths can be employed for different types of message switching
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Cited By (7)

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Publication number Priority date Publication date Assignee Title
US4608686A (en) * 1982-02-22 1986-08-26 Mitel Corporation Two wire voice and data subscriber loop
US4685123A (en) * 1985-09-13 1987-08-04 American Telephone And Telegraph Company Communication system having voice and data capability
US4916607A (en) * 1986-10-02 1990-04-10 Canon Kabushiki Kaisha Computer for executing a process control program and a communication control program in parallel
US5499285A (en) * 1991-11-12 1996-03-12 Microlog Corporation Automated telephone system with TDD capability
US5670957A (en) * 1991-11-12 1997-09-23 Microlog Corporation Methods for communicating with a telecommunications device for the deaf
US5408524A (en) * 1993-03-29 1995-04-18 Xel Communications, Inc. Answer supervision over pulse code modulated carrier system and method therefore
US6813353B1 (en) * 2000-04-12 2004-11-02 Adtran, Inc. Redundant operation of ring voltage generators utilizing voltage bus segmentation for fault isolation

Also Published As

Publication number Publication date
JPS58501532A (ja) 1983-09-08
GB2130845A (en) 1984-06-06
DE3267704D1 (en) 1986-01-09
KR880000961B1 (ko) 1988-06-04
WO1983001169A1 (en) 1983-03-31
ES515919A0 (es) 1983-12-16
KR840001976A (ko) 1984-06-07
EP0088786A4 (en) 1984-02-07
EP0088786A1 (en) 1983-09-21
ES8401815A1 (es) 1983-12-16
GB2130845B (en) 1985-10-09
EP0088786B1 (en) 1985-11-27
CA1177984A (en) 1984-11-13

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